During the process of electrolysis for the production of metals of the type indicated above, and in particular for the production of zinc and the like, a layer formed by sediments contained in the electrolyte, basically consisting of manganese dioxide (MnO), is deposited on the anode.
This layer grows thicker with time and acts as an electrical resistance. As the width of the layer increases so does the voltage required to cause a certain current to flow, which confirms that the deposit increases the consumption of electrical energy and should therefore be eliminated in the most effective way possible if the optimum conditions in the process of electrolysis are to be maintained.
Furthermore, the width of the layer increases in a uniform manner until it reaches a certain limit, after which kinds of trees are formed and which, once they have started, grow rapidly due to the fact that the conduction of current is greater through them as a result of the "points" effect and their increasingly shorter distance from the cathode.
When one of these points touches a cathode a short circuit is produced. This short circuit always damages the anode, causing torsions or holes which, apart from deteriorating the anode, mean that lead is transferred to the electrolyte and later deposited with the zinc, making the production thereof impure.
For these reasons, the anodes must be cleaned periodically in an effective and efficient way in order to ensure correct electrical behaviour and performance, and frequently enough to prevent the creation of possible short circuits which would contaminate the zinc deposits.
Various procedures for carrying out the cleaning of the anodes in order to prevent the above mentioned problems are already known and among them it is worth mentioning the following three:
a) By means of jets of water under pressure; PA1 b) By means of plates with flat opposing surfaces between which the anode is situated and pressed; PA1 c) By means of metal brushes.
The first of these systems requires equipment to supply water under pressure, said equipment requiring a high level of maintenance and giving rise to an excessive consumption of water. Furthermore, the level of noise during the cleaning process by means of the jets of water is high and in addition the result obtained is not totally satisfactory, due basically to the different adhesive forces of the deposits and the different forces with which the water impinges.
With the second of the systems mentioned, the cleaning operation is carried out by pressing the anodes between two plates with parallel surfaces. This action tries to break the deposits and detach them from the surface of the anode. Nevertheless, in many cases it causes the impurities to compact onto the anode until they are encrusted therein, making them practically impossible to eliminate.
Finally, in the third system mentioned the cleaning is carried out by eroding the deposits by the action of brushes with metal bristles. During the cleaning process a certain amount of erosion of the surface of the anode is also produced, giving rise to their premature deterioration. Similarly, when the brushes are in use the bristles wear away progressively. This wear is non-uniform which means that the subsequent action of the brushes on the anodes is non-uniform as well, giving rise to irregular cleaning.
Whichever cleaning system is used, the anode is subjected afterwards to a flattening process, since for the process of electrolysis the anodes and cathodes must have flat surfaces due to the proximity between them.